<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        h1 {
            color:red;
        }

        h1.c {
            color:blue;
        }

       

        h1.c#c2 {
            color:yellow;
        }

        span{
            color:purple;
        }

        #s1 {
            color:#0ff;
        }

      #c2  .s2 {
            color:#ccc;
        }

        /* 标签：1，id:100,class:10 */
    </style>
</head>
<body>
    <h1 class="c" id="c2"><span  id="s1" class="s2">css前戏</span></h1>
</body>
</html>